医网情深：结直肠癌患者的免疫组化筛查Lynch Syndrome——病理实习笔记（一） （刀评：ZL是本月来纽约实习病理/见习内科的CMG，在国外完成PhD，USMLE也取得很好的成绩。这是他第一周病理实习的家庭作业，写的很不错，内容全面、图文并茂、简洁明了。带实习过程中，我一直鼓励并要求实习医生把所看到的病例及时总结，写出笔记、小综述或文摘，锻炼他们写作能力。这样，进入住院医生培训后，除能很快适应工作，并尽快进入临床科研，写出文摘投交会议、文章投稿，以利于他们今后申请理想的fellowship。绝大多数实习医生都做的很好，而且进入住院医生培训后，也达到了我所期望的，很多人第一年就有会议文摘投交和/或文章投稿，有些已经完成著名大学单位的热门专业Fellowships，其中不乏常青藤名校。我为之骄傲。ZL很可能就是我最后一个所带的病理实习医生了，我希望也相信他会进入很好的病理住院医生培训单位） Mini-review: Screening of Lynch syndrome in patients with colorectal cancer using Immunohistochemistry ZL, MD, PhD   Lynch syndrome (LS) also known as hereditary non-polyposis colorectal cancer (HNPCC), is the most common cause of inherited colorectal cancer (CRC). The disease of LS was first recognized by a pathologist Dr. Aldred Scott Warthin, MD, Ph.D., at the University of Michigan a hundred years ago. It was further characterized by Dr. Henry T. Lynch, MD, later (1).   Patients with LS have a significantly increased risk for CRC and endometrial cancer as well as a risk of other malignancies in the ovary, stomach, small bowel, urinary tract, biliary tract, brain, skin, pancreas, and prostate. It accounts for about 3 percent of newly diagnosed CRC cases, and 8 percent of the incidence of CRC diagnosed under 50 years old (2). This autosomal dominant disorder is caused by a mutation in one of several DNA mismatch repair (MMR) genes, including MLH1, MSH2, MSH6, and PMS2. The MMRs can correct base-pairing errors such as base substitution or small insertion-deletion mismatches during DNA replication. The loss of these gene products results in defective MMR function, which drives carcinogenesis in Lynch syndrome (3). According to Dr. Hampel’s research, LS is largely under-recognized (4). Therefore, it is very important to screen LS in patients with colorectal cancer (CRC) or endometrial cancer before 50 years of age and familial clustering of Lynch-associated cancers. There are a few techniques available to identify Lynch syndrome. Compared to the methods such as multi-syndrome gene panel test, universal tumor-based genetic screening with MSI, or IHC testing of all CRCs regardless of age has slightly greater sensitivity for cost-effectively screening Lynch syndrome (5). The mutations in the MMR genes result in a truncated or missing MMR protein that can be detected as a loss of staining of the protein on tumor IHC testing, which has sensitivity and specificity of 83% and 89 %, respectively (6). IHC is inexpensive and readily available in community hospital settings, can be performed on small biopsies. Once the diagnosis of CRC was made by H.E. staining, tumor tissue should be sent for IHC on four MMR proteins, including MLH1, MSH2, MSH6, and PMS2 (7). Based on the IHC loss pattern, the decision can be made to move forward with more selective testing for Lynch syndrome (see the algorithm: Fig.1). IHC staining for the MMR proteins pattern is interpreted as follows (8): 1. Loss of MLH1 and PMS2 protein staining indicates a germline MLH1 mutation or MLH1 promoter hypermethylation. Additional testing (BRAF V600E mutation analysis or MLH1 hypermethylation analysis) can be used to distinguish between these possibilities. 2. Loss of PMS2 protein staining usually indicates a germline PMS2 mutation 3. Loss of MSH2 and MSH6 protein staining usually indicates a germline MSH2 mutation 4. Loss of MSH6 protein staining usually indicates a germline MSH6 mutation.   For example, during my externship with Dr. Gang He in New York, I saw a patient of 52-year old male who was found an ascending colon mass through colonoscopy. Biopsy confirmed the diagnosis of colorectal cancer by H.E. staining (Fig.2). Further testing demonstrated MSH2 (+), MSH6 (+), MLH1 (-), and PMS2 (-) in tumor cells (Fig.2), which indicates the presence of a germline MLH1 mutation or MLH1 promoter hypermethylation in this patient. Furthermore, a pathogenic germline mutation in the MMR is required for a definitive diagnosis of LS (9). The identification of germline MMR gene mutations significantly impacts the health care of patients with CRC and their families. A step-wise approach starting from IHC allows the efficient and cost-effective identification of LS.

Figure. 1 Approach to screening for Lynch syndrome in individuals with colorectal cancer ( from Uptodate.com)

Figure. 2 H&E and immunohistochemical staining of the ascending colon lesion. (A) H&E and immunohistochemical staining of (B) MSH2, (C) MSH6, (D) MLH1, and (E) PMS2 of the ascending colon lesion. Magnification, ×100 (Contributed by Gang He, MD, PhD)    Reference: 1. Boland, C.R., Lynch, H.T. The History of Lynch Syndrome. Familial Cancer 12, 145–157 (2013). 2. Win AK, Jenkins MA, Dowty JG, et al. Prevalence and Penetrance of Major Genes and Polygenes for Colorectal Cancer. Cancer Epidemiol Biomarkers Prev 2017; 26:404. 3. Moreira L, Balaguer F, Lindor N, et al. Identification of Lynch syndrome among patients with colorectal cancer. JAMA 2012; 308:1555. 4. Hampel H, de la Chapelle A. The search for unaffected individuals with Lynch syndrome: do the ends justify the means? Cancer Prev Res (Phila) 2011; 4:1. 5. Mvundura M, Grosse SD, Hampel H, Palomaki GE. The cost-effectiveness of genetic testing strategies for Lynch syndrome among newly diagnosed patients with colorectal cancer. Genet Med 2010; 12:93. 6. Weissman SM, Bellcross C, Bittner CC, et al. Genetic counseling considerations in the evaluation of families for Lynch syndrome--a review. J Genet Couns 2011; 20:5. 7. Hampel H, Frankel WL, Martin E, et al. Feasibility of screening for Lynch syndrome among patients with colorectal cancer. J Clin Oncol 2008; 26:5783. 8.https://www.lynchscreening.net/implementation/immunohistochemistry-ihc-only-2/ 9.https://www.cdc.gov/genomics/disease/colorectal_cancer/IHC.htm